The present invention relates to a process of decreasing the NO.sub.x content of the exhaust gases of cement-burning kilns by an addition of ammonia and/or ammonia-containing compounds to the hot exhaust gases, which are subsequently cooled with transfer of heat to the ground raw materials, dedusted in a manner known per se and finally desulfurized at 50.degree. to 100.degree. C. in a dry or semidry process by means of a mixture of raw cement powder and calcium hydroxide.
The elimination of nitrogen oxides in exhaust gases by an addition of ammonia and the desulfurization by calcium-containing substances are known (see Published German Application 35 26 008). The reactants are usually added in highly superstoichiometric proportions because it will not be possible otherwise to decrease the pollutant contents below the legally prescribed limits. If the reactants are separated from the exhaust gas stream regardless of whether or not they have been "consumed", is desulfurizing, the required surplus will primarily be an economic problem. If the reactants are gaseous, e.g., in the elimination of nitrogen oxides, an additional technological problem will arise because the ammonia added in a surplus is a pollutant in itself and, for instance in Switzerland, must not be emitted at a rate in excess of 30 mg/sm.sup.3 (sm.sup.3 =standard cubic meter).